CurtPalme.com Home Theater Forum

[gjaky]

I am playing with my 6PG xtra (with TAC4 lenses) and I realized that I can't focus the blue tube real sharp. I had an other topic about TAC4s so it is clear to me that is rather a low end lens.
The red tube is sharp, on the green I can't do as sharp image like with red, but also good, but the blue is a rubbish... I tried all sorts of electronic and manual focusing method, and I can't get a real sharp image (eg. with dot coarse pattern a blue dot is almost twice in diameter compared to a red dot) This is noticeable even in 480i.
I figured out that this may related to the wavelength of light, so thats why red and green is sharp (their wavelength are longer than blue and therefore they don't need a "higher" resolution lens.)
You can say why I messing with TAC4s, but I have a 9PG xtra too with original HD145N lenses and with that set I also noticed this symptom -however less.
This is a common problem or I do something wrong? Is there any solution for this? Mixing lenses should work? -like the blue lens should be replaced something more precise lens than HD145 (anyway what is better than HD145, which also fits to it's place?)

[Ile]

TAC4 sucks with blue, many have swapped only blue lens to HD6 to get better focus. With today HD6 prices swap all.

HD145N might have different throw distance than TAC4. If so, then blue picture will be wrong sized if only blue is swapped. HD145N is better and cost much more than HD6, least if you want color filtered (tinted) NEC version.

Blue should be leaved electrically unfocused to get more light output from tube and achieve good grayscale. That is why you see slight unfocus also in your other projector. Some projectors have circuit that prevent adjusting blue too sharp, your NEC might be one of those. Slight blue unfocus doesn't affect to overall sharpness of picture and you can't notice it to viewing distance.

There is only few high end projectors with blue gamma circuit to get proper grayscale without unfocus, but then tube will worn faster because it's needed to drive harder.

[stefuel]

There is a switch on the main board for "blue defocus"

[garyfritz]

Yes, is the blue defocus switch set? Blue is *supposed* to be defocused, to help color balance -- see e.g. http://www.avsforum.com/avs-vb/showthread.php?p=12844360#post12844360

Running with blue defocused results in slightly fuzzy blue, but the color balance is better. So if the defocus switch is set, the blue WILL be fuzzy, because it's electrically defocused.

But Ile may be right too. I don't see how/why a lens could be particularly bad for one color, but if lots of people have swapped them out and seen an improvement... BTW bad optical focus WON'T help the color balance. You have to defocus the blue electrically so the electron beam is spread over a larger area of phosphor.

[Ile]